The newly-discovered effect of high concentrations of magnesium ions on the fluorephore formation from catecholamines and indolamines has been characterized in more detail. Procedures for cryostat and Vibratome sectioning, utilizing the magnesium-catalysis, have been worked out, and we have also applied the methodology to young and embryonic rat brains with very good results. In a series of experiments now in progress we have discovered that other metal ions, having stronger Lewis' acid properties, have an even stronger catalytic effect than magnesium. This is particularly the case for aluminum ions. During the coming grant period we want (a) to characterize in more detail the mechanisms underlying the catalytic properties of metal ions, and (b) to work out fluroescence histochemical procedures for sensitive catecholamine and indolamine visualization using aluminium ions as catalytic agents. Our neuroanatomical studies on the detailed organization of the mesencephalic dopamine neurons projecting to the rat's forebrain have resulted in tree papers which are now about to be published. In the next step we now plan to proceed with a similar study on the monkey cerebral cortex. Finally, a study on the organization and function of the serotoninergic afferents to the inferior olive in the rat and cat has been initiated. These studies will attempt to analyze in some detail the serotoninergic mechanisms underlying the induction of tremorgenic activity in certain parts of the inferior olivary complex.